左右 literally means 'left and right', but as an adverb it functions like 'approximately' or 'about' — indicating an estimate or rough quantity, time, or degree. It reflects the idea of being near a value, neither strictly left nor right but somewhere in between, hence its figurative use for approximation. It’s commonly placed after numbers (especially cardinal numbers) and before measure words or nouns, such as 时间 (time), 岁 (years old), or 公里 (kilometers).

This term is neutral in register and widely used in both spoken and written Chinese — from casual conversation ('我等了二十分钟左右') to news reports ('人口约有14亿左右'). Unlike English 'around' or 'approximately', 左右 cannot begin a sentence or stand alone; it must attach directly to a numeral expression. It’s never used with exact values or absolutes, and it’s not appropriate in highly precise contexts like scientific measurements or legal documents.